1. Field of the Invention
The present invention relates to a data processing device such as a communication device for performing data processing using a central processing unit (CPU).
2. Description of the Related Art
FIG. 3 shows the construction of a PHS (Personal Handyphone System) 1, which is one example of a data processing device. Other examples of data processing devices include portable telephones, copy machines, facsimile machines, and the like.
The PHS 1 includes a radio frequency unit (RFU) 2, a baseband IC (BBIC) 3, a CPU 4, a flash memory 5, a DTE I/F (Data Terminal Equipment Interface) 6, and an antenna 7. The CPU 4 has a ROM (Read Only Memory) 8 incorporated therein. The mask-programmable type of ROM is widely used.
The ROM 8 includes at least a main program for the data processing procedure of the CPU 4 and other information such as information on functions (subroutine programs) used in the program, information on storage addresses of the functions or storage addresses of variables used in the program, and information on interrupt vectors for containing the addresses of interrupt routines of the CPU 4. The flash memory 5 also includes information for the data processing procedure. The flash memory is generally slower than ROM, but has the advantage of being rewritable.
When the antenna 7 receives a signal, the PHS 1 causes the RFU 2 and the BBIC 3 to extract predetermined information (data) from the received signal and output it to the CPU 4. The CPU 4 performs data processing based on the extracted information, information stored in the ROM 8, and information stored in the flash memory 5.
When the PHS 1 transmits information, the CPU 4 outputs the desired information to the BBIC 3. The BBIC 3 and the RFU 2 cause the information to modulate a transmission signal and then to be transmitted from the antenna 7.
The ROM 8 is a storage device in which high-speed data access can be performed. Accordingly, in order to achieve high-speed data processing, the main program for the CPU 4 and information on functions, storage addresses, and the like used in the program are provided in the ROM 8.
However, since the ROM 8 is a read-only storage device, information stored therein cannot be modified. Therefore, the data processing cannot be upgraded in the conventional PHS having the main program and the like stored in ROM, because the main program and the like cannot be modified.